This invention relates generally to apparatus for use in cleaning semiconductor wafers and more particularly to apparatus for use in cleaning wafers which protects the wafers from particle contamination during the cleaning process.
As is known, contaminates on the surface of a semiconductor wafer will adversely affect the electrical properties of the wafer. Therefore, it is of the utmost importance that the wafer surface be substantially free of particulate and other contaminates. Thus, at least the final stage of semiconductor wafer manufacture involves cleaning the wafer to remove the contaminates. Many methods are available for cleaning the wafers, including both chemical and mechanical processes as well as ultrasonic processes. Even with mechanical cleaning some liquids are used to facilitate the process. Therefore, it is always necessary to dry the wafers once cleaned.
The exacting standards of cleanliness required in the semiconductor industry (e.g., no more than 10 particles on the wafer greater than 0.2 micrometers in diameter) create unique problems for wafer cleaning. For example, the cleaning process itself can cause contaminates to deposit on the wafer surface as the wafer is handled. The conventional automated cleaning method processes wafers in a horizontal position. A wafer transport which holds the wafer as it is cleaned typically comprises a vacuum chuck or O-ring belt which engages one face of the wafer. Heretofore, the motors, belts, bearings and other mechanical parts used to clean the wafers were in close proximity to the wafer itself. These parts are sources of particulate and metallic contamination of the wafers in the cleaning apparatus. Moreover, the horizontal orientation of the wafers presents a large surface area perpendicular to the direction of flow of air through the cleaning apparatus. Thus, the surface is more likely to capture particles entrained in the air flow.
There are presently some vertical cleaning apparatus such as shown by Kudo et al., U.S. Pat. No. 5,317,778. However, the Kudo et al. apparatus receives wafers in a horizontal orientation and then moves them to a vertical orientation. As a result grippers having opposing members must be used to grip the wafers on opposing sides for moving them to a vertically upright position. The greater the area of the wafer contacted by the gripper member, the greater the chance for contamination of the wafer. Moreover, Kudo et al. rely upon infrared drying which evaporates liquid from the surface of the wafer. Evaporative drying leaves behind on the wafer contaminants which were suspended or dissolved in the wafer cleaning or rinsing liquids.